1. Field of the Invention
This invention relates to a soft magnetic film with compositional modulation, and a method of manufacturing the film. This invention also relates to a method of manufacturing a composition-modulated alloy film.
2. Description of the Prior Art
It is well-known in the art that "soft" is a term for defining a given magnetic property or characteristic of a substance.
Regarding magnetic heads for HDD's (hard disk drives), bulk heads have recently been replaced by thin-film magnetic heads. Generally, thin-film magnetic heads are manufactured by only thin-film forming processes. Thin-film magnetic heads include a coil, a coil insulating layer, and a film-shaped magnetic core. During the manufacture of the thin-film magnetic head, a soft magnetic film of the magnetic core is formed after the coil insulating layer is formed. Since the coil insulating layer is made of resin which will be deformed at a high temperature, it is necessary to form the soft magnetic film by a low temperature process. Accordingly, the formation of the soft magnetic film is usually based on electroplating. A typical soft magnetic film for a magnetic core is made of a permalloy (an Ni--Fe alloy).
A high recording density of a magnetic recording medium is desirable for a large-capacity and small-size HDD. A higher recording density generally requires a greater coercive force of a magnetic recording medium. To properly drive a magnetic recording medium having a great coercive force, it is good to increase the saturation magnetization of a soft magnetic film in a magnetic head. Accordingly, investigation has been given of cobalt-based soft magnetic films having great saturation magnetizations.
Electroplating is advantageous in that an apparatus for executing the electroplating is inexpensive. In addition, electroplating can be combined with photolithography. For example, during the manufacture of a thin-film magnetic head, a resin mask having a given magnetic core pattern is formed by photolithography, and then a soft magnetic film of the given magnetic core pattern is formed by electroplating while the resin mask is used. The photolithography enables a high accuracy of the shape of the soft magnetic film.
In thin-film magnetic heads, the volume of a film-shaped magnetic core is relatively small so that the sizes of magnetic domains in the core can not be ignored with respect to the size of the core. Thus, the characteristics of the thin-film magnetic heads are significantly affected by the behavior of magnetization in units of the magnetic domain sizes. During the operation of the thin-film magnetic head, the movement of magnetic domain walls causes "head noise". To suppress or prevent such head noise, it is effective to control the magnetic domain structure of the film-shaped magnetic core in the manufacture of the magnetic head.
A way of controlling the magnetic domain structure of the film-shaped magnetic core is to remove magnetic domains in a plane along the film of the core to provide a single-domain configuration. This way is effective especially in the case of a multilayer magnetic core having layers which are magnetically separated from each other in a direction along the thickness of the core. A known multilayer magnetic core has soft magnetic layers made of, for example, a permalloy, and nonmagnetic layers extending between the soft magnetic layers.
U.S. Pat. No. 4,869,971 discloses a process for electrodepositing a multilayer deposit on an electrically-conductive substrate from a single electrodeposition bath. The multilayer deposit includes a sequence of essentially repeating groups of layers. Each group of layers comprises a layer of a first electrodeposited material and a layer of a second electrodeposited material. The process in U.S. Pat. No. 4,869,971 includes the steps of immersing the substrate in an electrodeposition bath and repeatedly passing a charge burst of a first electric current and a second electric current through the electrodeposition bath to the substrate. The first electric current is a pulsed current with a first pulsed-on/off waveform and a first peak current density which is effective to electrodeposit the first electrodeposited material. The second electric current has a second waveform and a second current density which is effective to electrodeposit the second electrodeposited material. The duration of the charge bursts of the first and second electric currents is effective to form layers of the first and second electrodeposited material of desired thicknesses. U.S. Pat. No. 4,869,971 teaches that the copper contents of electrodeposited brass alloys vary as a function of the average current density of a plating current.